Kaizokugatari
by rick12
Summary: Nanami Yasuri thought that she could obtain peace in death by the hands of her brother, but even that wasn't likely. Finding herself in a new and completely different world, what would Nanami do with her second chance in life? Would she be able to find something to live for despite the agony that her body was constantly going through? NanamixLaw, Warning:Older/younger relationship.


**Hey, guys, this is rick12 and I have a story that I thought would be good. It's a crossover between Katanagatari and One Piece. I hope that you guys like it. Enjoy!**

 **Disclaimer: I do not own Katanagatari or One Piece. They belong to their respective owners. Still liked Mai Nakahara as Nanami Yasuri though!**

 **Kaizokugatari – Chapter 1**

 **Where Am I?**

 _'Where am I?'_ thought Nanami Yasuri softly as she looked around her surroundings, surroundings that were completing unfamiliar to her and were filled with trees. Nanami was a petite, slender girl with long, dark green hair that reached her lower back. Pink markings of cherry blossoms decorated her hair, with a pink flower-like clip coupling the lower ends of it into a ponytail. Her eyes were violet in color with white pupils. She had the appearance of a child, having a short height of about 5'1'', but she had a moderately-sized chest that was a high C-cup.

She was wearing a black yukata with long sleeves that had a purple-striped dress worn over it; the yutaka reached her ankles while the dress itself reached her knees. White Japanese arm bracers made of leather were worn on both of her arms. On her feet were a pair of white stockings with a pink band on them. She wore simple sandals as footwear. To finish her appearance, she had a pink band wrapped around her slender neck. All in all, Nanami was a Japanese beauty despite her child-like appearance, even though she was actually 30-years-old.

 _'The last thing that I remembered was Shichika killing me and granting me the death that I wanted... so why am I still alive? And just what is this place?'_ Nanami questioned in confusion. She was sure that she was killed by the hands of her younger brother, and yet here she was, alive and kicking. Her body was just as frail and weak as she remembered from her birth, and it was still feeling pain from her illness caused by her overwhelming power, even though she was used to it. Her body was extremely resilient and refused to die despite the pain it brought her, having the unnatural ability to recover from severe injuries and lethal poisons in a matter of moments. She looked under her yukata to see if the fatal wound inflicted by her younger brother was still there. However, there was no wound or scar on her chest, just perfect pale skin. Even though she didn't express it, she was shocked from seeing the lack of a gaping hole in her chest.

 _'What? Even if it did healed, the wound would had left a scar. What was able to heal me to the point of not leaving a scar,'_ Even though she was very intelligent and cunning under her gentle exterior, Nanami wasn't able to come to a logical conclusion about why she was still alive, and more importantly, how she was in a different place. This definitely wasn't where she remembered dying in. _'I wonder if I retained all my abilities...'_ She was curious if she still retained her abilities, both natural and copied (and mastered), after she was supposedly killed by Shichika. Nanami planned on testing this out before eventually investigating about her mysterious circumstances.

She then proceeded to perform all the techniques and abilities, genetic or not, that she copied and mastered with the **Higi: Migeika (Hidden Technique: Sight Training)** , which was her unique ability that she still possessed, in an open area. First was all the techniques that was associated with her family's style, **Kyotoryu (Swordless Style)** , which she did with more skill and power than her younger brother could ever achieve. **Kyotoryu** turned the user's arms and legs into deadly weapons (they don't physically transform) that could easily cut through practically anything like butter, since the Yasuri family was incapable of using actual swords. She even performed one technique that she invented herself. Second was the three **Ninpo** that she copied and mastered from those three Maniwa ninja that she killed brutally when they tried to kidnap her from Yasuri Island: one allowed her to lengthen and strengthen her nails into deadly claws, another allowed her to make her weightless, and the other allowed her to make and launch small caltrops that were hook-tipped and laced with poison that could immobilize others and cause them intense pain. Third was the Superhuman Strength and Speed of an adult Itezora male that she was able to copy after she massacred the entire Itezora clan except for Konayuki. She was able to copy these two passive abilities even though they were genetic in nature and inherent to the Itezora. These two genetic abilities boosted her already high and unnatural strength and speed to extreme levels to the point that it became terrifying.

Nanami realized that she retained her fast reflexes, keen senses, and the ability to think ahead in battle. Her **Higi: Migeika** only boosted her reflexes and already Immense Speed (stacked with the Superhuman Strength and Speed from the Itezora along with her (un)natural speed before she left Yasuri Island) even further. The most fearsome aspect of **Higi: Migeika** was that Nanami could see through any technique, movement, or weaknesses, allowing her to master any technique just by seeing it with her eyes. With this unique ability, she could perfectly copy any technique, regardless if it was genetic in nature or not, by seeing it once and adding it as her own. If she saw the same technique twice, she would master it and could combine it with other moves that she learned. Not only that, thanks to **Migeika** , she could literally predict the attacks of any martial art by just seeing the stance that her enemies would take. It was because of this that Nanami never took a stance herself. She could only use her full power for a limited time due to her frail body, however. All of this made Nanami a complete hellish nightmare to fight against, even if her opponents took them into account.

Seeing that she still possessed all of her current abilities immediately before her supposed death by her brother's hands, she sat down where she was testing her abilities, which was filled with some trees smashed to oblivion and others slashed cleanly into pieces like a hot knife through butter. One tree had 272 or more deep imprints on it to the point that it looked like a toothpick. Even the ground had huge, deep craters imprinted on them. _'Even though I have all of my current abilities, I still don't understand why I'm alive. Is this another chance at life? I don't know.'_ Nanami was comprehending about her current situation. Even though she didn't know why she was still alive with this cursed body, she knew that she must look for answers, even in this unknown world. She would then live a new life in this new world once she had found her answers.

 _'Even so, I should begin exploring this place. It might give me answers on where I am,'_ With that thought in mind, Nanami stood up from where she was sitting and began walking toward a random direction to see where she was. After walking for a few minutes, she reached what looked like the edge of an island due to seeing a large body of water. _'It looks like I'm on some sort of island, and it seems that it has no human activity from what I can see... hmm?'_ Nanami heard what seemed to be shouts and battle-cries, and judging by how loud it was, she was close to the source. Seeing a chance for information, she walked towards the location of the disturbance which she found moments later via her very sharp senses. What she found was interesting to her: men in white uniforms were fighting against people that looked like bandits from how they were dressed. She saw a man that wore different clothing from the white-uniformed men, who she assumed was their commander. He wore a white trench-coat that had the kanji for 'Justice' on the back like a cape. His face was muscular-looking, but it was nothing unique. She also sensed the leader of the bandits, who was wearing a black trench-coat; he was also not unique compared to the marine commander.

 _'Hmm? A fight? Maybe I'll ask them about where I am...'_ Nanami then proceeded to walk right into the fray, which caused every combatant to pause on their fighting to look at her.

"Who are you, bitch!?" one of the bandit-looking men rudely demanded from her, which only caused her to raise one of her eyebrows in curiosity.

"Hello. Do any of you know what this place is?" Nanami asked the marines and bandit-looking men politely. This caused the bandits to laugh hysterically while the marines just looked at her in shock to her question.

"Why the fuck should we tell you, little girl!? You're in our way of fighting these white-wearing pricks! We'll teach you not to mess with us pirates! Time to die!" the now-named pirate that insulted her earlier yelled angrily before charging at the seemingly defenseless girl, sword raised with the intent to kill her. However, just before his weapon could even reach her, Nanami's hand lashed out with speeds that were untraceable to everyone to catch the blade with sheer ease, stopping it mere inches from her face. Even though she caught it by the sharp edge, her hand had no scratches on it whatsoever from the grab.

"W-what...?" the pirate muttered in shock when he saw the girl stopping his sword with her bare hand with no damage.

"Well, sir... can you die?" Nanami asked with no emotion before she plunged her free hand right into the man's chest where his heart was located, causing a large hole to appear where the area used to be. A large amount of blood splattered across the ground, making a pool of blood grow around the pirate. His eyes widened in fear and agony, coughing up copious amounts of blood before she retracted her hand, which was now covered in blood, from his chest. The pirate wobbled for a few seconds before he fell onto the ground, dead and with a terrified expression on his frozen face. Everyone, including the marine commander and pirate captain, were frozen in shock and horror at the brutality of the pirate's death. Sure, they experienced death before, but this was the first time that they saw anyone dying a terrible death.

The surrounding pirates' feelings of shock then shifted to anger when one of their own was killed by Nanami. "You'll pay for that!" All of the pirates, except their captain, shouted in anger before mindlessly charging Nanami, forgetting about how she caught sharp weapons with her bare hand.

"Useless... you'll never win like that..." Nanami said under her breath, letting a sinister smirk appear on her face. What a bunch of fools, charging toward their own slaughter. She vanished from her spot using her sheer speed and appeared right in the middle of the pirate mob before punching the nearest pirate in the chest, sending him flying while breaking every bone in his chest with her sheer strength, even though she held back heavily on that punch. Before any of the other pirates could react, Nanami's arms blurred with uncanny speed and grace before she stopped, her hands positioned like a knife. It was silent for a few seconds before something horrible happened. All of the remaining pirates, except their captain who didn't charged recklessly at her, had thick red lines through their bodies before they literally fell apart in pieces, dead before they could even register the pain of being torn to pieces. Blood, organs, and even brain matter splattered upon the ground, spraying all over the place like a water fountain. Parts of their mutilated bodies landed on the ground with a sickening splat. It was like a scene out of a horror movie, only that this was real. The marines, their commander, and the pirate captain had pale faces from the brutal slaughter of the pirates. Nanami, however, was barely fazed by what she did. In fact, her expression was completely stoic.

"Now... Will you tell me where I am?" Nanami requested politely in a calm manner, freaking out everyone from her tone of voice. What the hell was she!? How could she stay calm from slaughtering those men, even if they were pirates!?

"Y-you bitch! I'm going to kill you for killing all my comrades!" The pirate captain roared out angrily before he pulled out a two-handed ax from his back. He proceeded to charge at her, rage clouding his mind and not even considering that he would die like the rest of his deceased comrades. Nanami made no expression at his declaration for revenge before he side-stepped a swing from him and chopped both of his arms off by the forearm with her hand. The captain screamed in agony before he was 'lightly' punched in the stomach, doubling him over before his neck was grabbed by the small girl.

"Can you now tell me where I am?" Nanami asked stoically while giving him a blank, cold stare that caused the now-armless captain to sweat in dread from the stare.

"Y-you're on an island which was my hideout." The scared man stuttered. He was now afraid of this weak-looking girl who slaughtered his whole crew. Perhaps if he answered her questions, he could be spared.

"I see... Do you know where the nearest town is?" Nanami asked him another question. She hypothesized that the bleeding captain didn't have any more information that would be useful to her, so she would just ask him this last question and then proceed to kill him.

"N-no. There aren't any towns on this island. Please... let me go." The pirate captain begged. He didn't want to die like his crew to this insane girl.

"Oh? Then you're no use to me. Good-bye, sir." Nanami said eerily before she increased her grip on the man's throat to steel-crushing levels, crushing his neck in a split second with no remorse. She dropped the dead body like a sack of potatoes before contemplating on her next move. Realizing that the marines were still there, she thought that they could be more helpful with her questions than those idiots that she killed. She faced the marines, causing them to tense up in anxiety on what she would do.

"Hello. Can you tell me where the nearest town is?" Nanami requested the marines politely, but it didn't lower their tensed bodies. After a few seconds, the marine commander decided to answer her question, realizing that he didn't want his men to suffer the same fate as those pirates.

"Y-yes, the nearest town is on another island north of this one." The commander said politely while pointing towards the north via his compass.

"Are you sure?" Nanami questioned curiously. She wanted to make sure that the marine wasn't lying about his directions.

"Y-yes, if you go towards the direction where I'm pointing, you'll be able to get to the island that the town is located on a boat." The commander said, not wanting to risk lying to the girl.

"Okay. Thank you for your time." Nanami replied in gratitude. Now that she got the directions, it was time for her to look for answers in the town that that man told her about. She might be able to find an information center of sorts there. She turned around and started to head to the north of this island before the commander's voice called out to her.

"Wait! What's your name!?" The marine captain asked her. He needed to know who she was in order to tell his superiors, the World Government, about her. She killed those pirates without effort or remorse, so it would be best to warn the World Government about her.

 _'Hmm,'_ Nanami wondered if she should reveal her name to his stranger. She didn't see what this would lead to, but she was curious about why the man was asking her name. Perhaps to tell his boss? Nevertheless, she would give it to him to see where it would lead to.

"My name is Nanami. Nanami Yasuri. Good-bye." Nanami replied before she disappeared into the forest without a trace. The marines relaxed after she left, with the commander replaying her name in his name in his mind. After a few seconds, he ordered his men to go back to their ship and call for the clean-up crew to gather the pirates' corpses.

 _'Nanami Yasuri... I got a very horrible feeling that she will change this world heavily.'_ The commander thought with dread before going back to his ship; he got a lot of work to do, especially with reporting to his superiors about those pirates' deaths and that girl.

* * *

 **10 minutes later...**

Nanami was able to reach the very north end of the island she was on. The town was on another island north of this one, meaning that she had to cross this sea to get there. Too bad for anyone that she had the ability to make herself weightless and thus walk on water. "It's time to go," Nanami said before she stepped on the surface of the water. _**'Ninpo: Ashigaru.'**_ Nanami activated the technique, making herself weightless in order to stand on the water.

She then proceeded to go on her way towards north, walking at a leisurely pace on the water's surface. She was in no hurry to get to the town; she could afford to enjoy a casual walk across this sea and see what this world had to offer along the way to her destination. Nanami smiled at this, wondering about how this new life would turn out for her. Her smile became sinister at the thought as she walked.

What will happen to the world of One Piece now that Nanami was here?

 **Chapter End.**

 **A/N: So, how did the first chapter go? This was only the Introductory Chapter, to explain about the circumstances that our main (villain?) protagonist is in, and her search for reasons on why she was in this new world.**

 **You can bet that the protagonist is Nanami Yasuri from Katanagatari, a light novel series that was faithfully adapted into an anime series. I recommend watching it, it's quite good. By the way, everything said about Nanami's abilities in this chapter were SHOWN in Katanagatari canon; she does show the ability to copy any technique/ability she sees once while mastering them if she sees them twice, along with her natural abilities that supplement her.**

 **This happened in Episodes 4 and 7 of the anime, where Episode 7 explained that she could EVEN COPY abilities that were GENETIC in nature, such as the Itezora clan's Superhuman Strength that was inherent to them genetically; she copied the highest form of Superhuman Strength that the Itezora had, which was the strength of a full-grown adult Itezora male. She now has the Superhuman Strength and Speed of an adult Itezora male, boosting her natural physical strength and speed to extremely frightening levels, making her even deadlier and more badass than before she left her home. I pity those that would take her hits.**

 **Anyway, this takes place about 26 years before One Piece canon, when Trafalgar Law was born. I'm thinking about pairing Nanami with Law; their first meeting could be years before his home country's destruction but 5 years after his birth. Law could grow on Nanami, letting her realize that there were good things in this world despite the constant agony that her ill and frail body goes through from her power.**

 **I hope to see you guys later in the next chapter. Please, no flames or I WILL block you for wasting my time with reading your insults.**


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